1. Field of the Invention
This invention relates to a method for producing a rubber melt and apparatus therefor, and more particularly, it relates to a method and apparatus for producing a rubber melt of high industrial utility by treating rubber both mechanically and thermally.
2. Description of the Prior Art
Rubber waste comprising waste tires mainly is now posing a serious social problem along with plastic waste. Although many and extensive studies are being made in search for an effective way for disposal or utilization of such rubber waste, there is yet available no effective and economical method for mass utilization of such rubber waste, except for processing the same into reclaimed rubber, and the bulk of rubber waste is either buried in the ground or incinerated. Under such circumstances, it is a desideratum to develop a method and apparatus for enabling the effective recycling of rubber waste, the main source of which is waste tires.
Recently, attention has been directed to a dry distillation method (such as proposed in Japanese Patent Publication No. 8354/77) as an effective means for the treatment of rubber waste. According to this method, vulcanized rubber is thermally decomposed at 300.degree.-700.degree. C. to separate it into three phases, that is, gas, oil and solid residue, the gas and oil of which are put to reuse as fuel while the solid residue is utilized as various types of useful carbon materials or as coke fuel. This method, however, is low in throughput capacity for its vast equipment and maintenance costs and the estimated value of the products is also low. Therefore, said method has an economical problem.
In order to solve these problems, there has been proposed a method which is totally different in principle from such conventional methods, that is, a method in which a screw extruder is used for producing a vulcanized rubber melt (Japanese Patent Publication No. 43873/76). The point of this new method is that vulcanized rubber is heated in a screw extruder together with at least 25 parts by weight of a heavy oil or the thus obtained vulcanized rubber melt per 100 parts by weight of said rubber at a temperature of 310.degree.-380.degree. C. in the presence of air to decompose the vulcanized rubber. According to this method, however, the heavy oil or vulcanized rubber melt must be added in an amount of at least 25 parts by weight per 100 parts by weight of the vulcanized rubber, and therefore, there are required means for supplying such a heavy oil or for recycling the melt, and further, the substantial throughput of vulcanized rubber is limited.
The most important factors in melting the rubber by a screw extruder are that the produced melt has a moderate viscosity and that the degree of melting is as high as substantially 100%.
When the melt viscosity is too high, a problem is caused in treatment of the melt in some uses, while a low degree of melting, which means the existence of non-melted matters, brings about an unfavorable result in use of the rubber melt. Particularly when such a melt is used as a rubber compounding agent, the existence of the non-melted matters may cause a deterioration in physical properties.